|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] xen-unstable, winxp32 very poor performance on AMD FX-8150, I bisected and changeset is 24770:7f79475d3de7
On Nov 1, 2012, at 1:00 PM, Tim Deegan <tim@xxxxxxx> wrote:
> Hi,
>
> At 14:59 +0100 on 22 Oct (1350917960), Tim Deegan wrote:
>> At 19:21 +0200 on 20 Oct (1350760876), Peter Maloney wrote:
>>> The change was 8 months ago
>>>
>>> changeset: 24770:7f79475d3de7
>>> user: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
>>> date: Fri Feb 10 16:07:07 2012 +0000
>>> summary: x86/mm: Make p2m lookups fully synchronized wrt modifications
>>
>> This change was bad for performnace across the board and most of it has
>> since been either reverted or amended, but clearly we missed something
>> here.
>>
>> It's interesting that Win8 isn't slowed down. I wonder whether that's to
>> do with the way it drives the VGA card -- IIRC it uses a generic VESA
>> driver rather than a Cirrus one.
>
> In fact this is to do with the APIC. On my test system, a busy 2-vcpu
> VM is making about 300k/s accesses to the APIC TPR. These accesses are
> all trapped and emulated by Xen, and that emulation has got more
> expensive as part of this change.
>
> Later Windows OSes have a feature called 'lazy IRQL' which makes those
> accesses go away, but sadly that's not been done for WinXP. On modern
> Intel CPUs, the hardware acceleration for TPR accesses works for XP; on
> AMD it requires the OS to use 'MOV reg32, CR8' to access the TPR instead
> of MMIO, which XP is clearly not doing. :(
>
> Peter: if you have the option, you might find that installing the PV
> drivers that ship with Citrix XenServer 6.0 makes things work better.
>
> Andres: even though this load of APIC emulations is pretty extreme, it's
> surprising that the VM runs faster on shadow pagetables! Any ideas for
> where this slowdown is coming from?
Not any immediate ideas without profiling.
However, most callers of hvmemul_do_io pass a stub zero ram_gpa address. We
might be madly hitting the p2m locks for no reason there.
How about the following patch, Peter, Tim?
diff -r 5171750d133e xen/arch/x86/hvm/emulate.c
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -60,24 +60,28 @@ static int hvmemul_do_io(
ioreq_t *p = get_ioreq(curr);
unsigned long ram_gfn = paddr_to_pfn(ram_gpa);
p2m_type_t p2mt;
- struct page_info *ram_page;
+ struct page_info *ram_page = NULL;
int rc;
/* Check for paged out page */
- ram_page = get_page_from_gfn(curr->domain, ram_gfn, &p2mt, P2M_UNSHARE);
- if ( p2m_is_paging(p2mt) )
+ if ( ram_gpa != INVALID_MFN )
{
- if ( ram_page )
- put_page(ram_page);
- p2m_mem_paging_populate(curr->domain, ram_gfn);
- return X86EMUL_RETRY;
- }
- if ( p2m_is_shared(p2mt) )
- {
- if ( ram_page )
- put_page(ram_page);
- return X86EMUL_RETRY;
- }
+ ram_page = get_page_from_gfn(curr->domain, ram_gfn, &p2mt,
P2M_UNSHARE);
+ if ( p2m_is_paging(p2mt) )
+ {
+ if ( ram_page )
+ put_page(ram_page);
+ p2m_mem_paging_populate(curr->domain, ram_gfn);
+ return X86EMUL_RETRY;
+ }
+ if ( p2m_is_shared(p2mt) )
+ {
+ if ( ram_page )
+ put_page(ram_page);
+ return X86EMUL_RETRY;
+ }
+ } else
+ value = 0; /* for pvalue */
/*
* Weird-sized accesses have undefined behaviour: we discard writes
@@ -455,7 +459,7 @@ static int __hvmemul_read(
return X86EMUL_UNHANDLEABLE;
gpa = (((paddr_t)vio->mmio_gpfn << PAGE_SHIFT) | off);
if ( (off + bytes) <= PAGE_SIZE )
- return hvmemul_do_mmio(gpa, &reps, bytes, 0,
+ return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
IOREQ_READ, 0, p_data);
}
@@ -480,7 +484,8 @@ static int __hvmemul_read(
addr, &gpa, bytes, &reps, pfec, hvmemul_ctxt);
if ( rc != X86EMUL_OKAY )
return rc;
- return hvmemul_do_mmio(gpa, &reps, bytes, 0, IOREQ_READ, 0, p_data);
+ return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
+ IOREQ_READ, 0, p_data);
case HVMCOPY_gfn_paged_out:
return X86EMUL_RETRY;
case HVMCOPY_gfn_shared:
@@ -552,7 +557,7 @@ static int hvmemul_write(
unsigned int off = addr & (PAGE_SIZE - 1);
gpa = (((paddr_t)vio->mmio_gpfn << PAGE_SHIFT) | off);
if ( (off + bytes) <= PAGE_SIZE )
- return hvmemul_do_mmio(gpa, &reps, bytes, 0,
+ return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
IOREQ_WRITE, 0, p_data);
}
@@ -573,7 +578,7 @@ static int hvmemul_write(
addr, &gpa, bytes, &reps, pfec, hvmemul_ctxt);
if ( rc != X86EMUL_OKAY )
return rc;
- return hvmemul_do_mmio(gpa, &reps, bytes, 0,
+ return hvmemul_do_mmio(gpa, &reps, bytes, INVALID_MFN,
IOREQ_WRITE, 0, p_data);
case HVMCOPY_gfn_paged_out:
return X86EMUL_RETRY;
@@ -804,7 +809,7 @@ static int hvmemul_read_io(
{
unsigned long reps = 1;
*val = 0;
- return hvmemul_do_pio(port, &reps, bytes, 0, IOREQ_READ, 0, val);
+ return hvmemul_do_pio(port, &reps, bytes, INVALID_MFN, IOREQ_READ, 0, val);
}
static int hvmemul_write_io(
@@ -814,7 +819,7 @@ static int hvmemul_write_io(
struct x86_emulate_ctxt *ctxt)
{
unsigned long reps = 1;
- return hvmemul_do_pio(port, &reps, bytes, 0, IOREQ_WRITE, 0, &val);
+ return hvmemul_do_pio(port, &reps, bytes, INVALID_MFN, IOREQ_WRITE, 0,
&val);
}
static int hvmemul_read_cr(
diff -r 5171750d133e xen/arch/x86/hvm/io.c
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -231,7 +231,7 @@ int handle_pio(uint16_t port, int size,
if ( dir == IOREQ_WRITE )
data = guest_cpu_user_regs()->eax;
- rc = hvmemul_do_pio(port, &reps, size, 0, dir, 0, &data);
+ rc = hvmemul_do_pio(port, &reps, size, INVALID_MFN, dir, 0, &data);
switch ( rc )
{
>
> Cheers,
>
> Tim.
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel
|
 |
Lists.xenproject.org is hosted with RackSpace, monitoring our |